This invention relates to a method for coating components of gas turbine engines, such as by aluminide coating, heat treating the components, and rapidly quenching the components in a combined operation using a single apparatus.
To provide protection against high temperature oxidation and hot corrosion, components of gas turbine engines such as turbine airfoils are subjected to, for example, diffusion aluminide coating. Diffusion coatings are imparted by a thermal/chemical reaction process typically requiring a reducing or inert atmosphere at an elevated temperature. A diffusion aluminide coating, for example, may be imparted at roughly 1975xc2x0 F. (1080xc2x0 C.).
Engine components are often strengthened after diffusion coating by being subjected to aging. In order to optimize these aging effects, it is necessary to first set the gxe2x80x2 (gamma prime) phase by quenching the components rapidly to below the age temperature after holding the component steady for, for example, 4 hours, at the alloy solution temperature. Heretofore, it has only been possible to achieve the quench rate necessary to set the gxe2x80x2 phase by using a vacuum furnace. Such furnaces have not been employed for coating operations because the byproducts from such operations damage the furnace""s ability to maintain desired vacuum level. Furnaces suitable for coating operations have not been able to achieve the rapid quench rate required to set the gxe2x80x2 phase. Diffusion coating furnaces have not been capable of quenching the components to below the age temperature sufficiently rapidly. As such, aluminide coated components have been coated in a diffusion coating furnace, allowed to cool, removed from the diffusion coating furnace, placed in a heat treatment furnace, heated to the solution temperature, held at that temperature for the required time period, then rapidly quenched.
Briefly, therefore, the invention is directed to a method for imparting an aluminide coating to an alloy gas turbine engine component, heat treating the component, and quenching the component by exposing the component to a source of aluminum at an elevated temperature in a coating furnace to deposit an aluminum-based oxidation barrier on the component, heating the component in the coating furnace to a temperature of at least the solution temperature of the alloy, and quenching the component by flowing an inert gas around the component in the coating furnace to cool the component from the temperature of at least the solution temperature of the alloy to a temperature at which a gammaxe2x80x2 phase of the alloy is set in the alloy in less than about 10 minutes.
In another aspect, the invention is directed to a method for imparting an aluminide coating to alloy gas turbine engine components, heat treating the components, and quenching the components, all in a coating vessel of a coating furnace such that the ratio of the mass of the components to the volume of the coating vessel is less than about 12 lbs/cubic foot (200 kg/cubic meter).
The invention is further directed to a method for imparting an aluminide coating to a plurality of Ni-based alloy gas turbine engine components, heat treating the components, and quenching the components in which the components are arranged irregularly with respect to each other in a coating can in a coating furnace to reduce reflection of heat between said components, thereby facilitating rapid quenching.